thats only if they eat way too much. If you eat too much of ANYTHING it can be harmful....you can eat or drink yourself to death with anything. The only way grit impaction would happen is if the owner provided unlimited amounts and not enough food or if the bird had a psychological problem. But they even said they only give their bird a little grit and that cannot be harmful. Thats like saying oh well you said its safe to drink water but people can die from water. You read too much into things.